Donald J. Trump said he would not rule out an effort to remove Representative Paul D. Ryan as chairman of the Republican National Convention if he did not endorse Mr. Trump’s candidacy.

Mr. Trump stopped short of calling for Mr. Ryan, the speaker of the House, to step down from his convention role. But in an interview that aired Sunday on NBC’s “Meet the Press,” Mr. Trump said there could be consequences in the event that Mr. Ryan continued withholding his support.

“I will give you a very solid answer, if that happens, about one minute after that happens, O.K.?” Mr. Trump said. “There’s no reason to give it right now, but I’ll be very quick with the answer.”

Mr. Trump has shown little interest over the last few days in placating his critics inside the party, including Mr. Ryan. Mr. Ryan, a representative from Wisconsin, said on Thursday that he was not ready to endorse Mr. Trump, citing reservations about his political style and policy agenda. The two men are scheduled to meet privately in Washington next week.

But on “Meet the Press,” Mr. Trump struck a dismissive tone toward Mr. Ryan and responded with outright hostility to other Republican critics who have refused to back his campaign.

Jeb Bush, he said, was “not honorable” for breaking his promise to endorse the party’s nominee. Mitt Romney, he said, was “ungrateful” for the help Mr. Trump gave him in the 2012 election. Mr. Trump referred to Lindsey Graham, the South Carolina senator who said Friday he would never vote for Mr. Trump, as “this lightweight.”

Of Mr. Ryan, he said: “I’d like to have his support. But if he doesn’t want to support me, that’s fine, and we have to go about it.”

Other allies of Mr. Trump have gone further in criticizing Mr. Ryan for declining to issue an immediate endorsement.

Sarah Palin, the former Alaska governor, predicted in an interview on CNN’s “State of the Union” that Mr. Ryan would be “Cantored,” a reference to former Representative Eric Cantor of Virginia, who was in line to be speaker of the House before losing re-election in a Republican primary in 2014.